In recent years, non-contact communication systems each utilizing NFC (Near Field Communication) that is a short-distance non-contact communication technology have become significantly widespread. In such a non-contact communication system, a transmission signal output from a transmission antenna (resonant circuit) of a reader/writer (hereinafter, referred to as R/W) apparatus dedicated to the system is received by a reception antenna, which provided in a non-contact IC (Integrated circuit) card, using an electromagnetic induction action.
In such a non-contact communication system, for obtaining satisfactory communication characteristics, it is important that a frequency of a signal source in the R/W apparatus, a resonant frequency of the transmission antenna of the R/W apparatus, and a resonant frequency of the reception antenna (resonant circuit) in the non-contact IC card are equal. However, the resonant frequency of the reception antenna of the non-contact IC card or the transmission antenna of the R/W apparatus fluctuates due to various factors. It makes it difficult to stably transmit/receive information between the non-contact IC card and the R/W apparatus.
In view of this, in the technological field of the non-contact communication system, various technologies for maintaining a satisfactory communication state under any conditions have been proposed. Patent Literature 1 has disclosed a technology of achieving optimization of communication characteristics while monitoring a communication state as a transmission apparatus that performs non-contact communication with an outside by an electromagnetic induction action, as a configuration including a transmission antenna, a signal output unit, a monitor circuit unit, and a correction circuit unit.
In this transmission apparatus, the monitor circuit unit monitors information regarding a current flowing through an antenna coil and determines a communication state on the basis of the monitored information, and the correction circuit unit corrects the communication characteristics on the basis of a result of determination of the monitor circuit unit (e.g., see paragraph [0137] of Patent Literature 1).